1. Field of the Invention
The present invention relates to a bearing case for securely accommodating a bearing for supporting a crankshaft of an engine.
2. Description of the Related Art
General-purpose engines of an overhead valve (OHV) type or an overhead camshaft (OHC) type are widely used as power sources for lawn mowers, power-driven sprayers, generators, and others. The crankshaft of such engines is generally supported by ball bearings (hereinafter referred to simply as xe2x80x9cbearingxe2x80x9d). In most cases, the crankshaft is supported at both ends thereof by the bearings.
The bearings are held by a crankcase and a main bearing case (hereinafter referred to simply as xe2x80x9cbearing casexe2x80x9d) mounted thereto. Generally, the bearing on one side is accommodated in and held by a bearing holder provided at a wall of the crankcase, while the other bearing is accommodated in and held by the bearing case.
FIG. 6 is a cross-sectional view showing a structure of an engine using a conventional bearing case. The conventional bearing case 100 includes a bearing holder 102 protruded at the center of a side wall 101 thereof as shown in FIG. 6. Along an outer periphery of the bearing case 100 is formed a crankcase mounting section 103 (hereinafter referred to simply as xe2x80x9cmounting sectionxe2x80x9d) which is to be joined to a cover mounting surface of the crankcase through a gasket. A hollow 104 is formed between the mounting section 103 and the bearing holder 102. The bearing holder 102 accommodates a ball bearing (not shown) therein and thereby supports one end of the crankshaft.
The engine as shown in FIG. 6 includes an oil pan 107 formed in a lower portion of the crankcase 106, where a lubricating oil 108 is stored. The lubricating oil 108 is picked up by an oil dipper 110 with a rotation of the crankshaft 109, droplets of which lubricates a valve-operating system such as a chain and sprockets (both not shown).
The crankshaft is subjected to a force exerted orthogonally to an axial direction thereof also in an explosion stroke. The bearing accordingly receives the force exerted thereto in a radial direction orthogonal to the crankshaft in addition to the force in a rotational direction thereof. The bearing case 100 shown in FIG. 6 receives such force by just the bearing holder 102.
In the bearing case 100, however, the mounting section 103 overhangs from the bearing holder 102, and thus when subjected to a radially acting force, the bearing holder 102 warps from its base end, resulting in deformation in the side wall 101. The radially exerted force also acts on the mounting section 103 as moment, whereupon a compressive force and a shearing force act between the mounting section 103 and the crankcase 106. The gasket interposed therebetween is subjected to such forces repeatedly and is accordingly deformed over and over again. Thus, deterioration of the gasket proceeds quickly, leading to the risk of oil leakage.
In the high-performance engines with higher speed for higher output in recent years, the bearing holder 102 is subjected to ever increasing load. The bearing case shown in FIG. 6 is hardly capable of withstanding such load, and therefore an improvement in the structure of bearing case has been desired.
On the other hand, when the engine of FIG. 6 is inclined and located on a slope, an oil surface of the lubricating oil 108 stored in the crankcase 106 is inclined as shown by a dotted line in FIG. 6. In short, the lubricating oil 108 enters an hollow forming a part of an oil pan in a lower portion of the bearing case 100 more and more by the inclination, whereby a slope of the oil surface is formed at a right side of the oil pan. Thus, the oil dipper 110 results in no-touch with the oil surface, so that the lubricating oil 108 can not be fully supplied to the valve operating system.
An object of the present invention is to provide a bearing case with more rigidity which secures a valve-operating system to be fully lubricated even when the engine is located with inclination.
In order to achieve the object, there is provided a bearing case attached to a crankcase of an engine in order to hold a bearing for supporting a crankshaft of the engine, comprising a bearing holder for holding the bearing, a crankcase mounting section formed on an outer peripheral surface of the bearing case to be joined to the crankcase, and rib walls formed so as to surround the bearing holder and extend from the bearing holder to the crankcase mounting section, wherein the rib walls are located adjacently to a side end surface of a crankcase.
According to the present invention, a force acting on the bearing holder in a radial direction from the crankshaft is received by rib walls, so that the bearing holder can be prevented from warping at its base end as the conventional bearing case. Also, the crankcase mounting section receives less moment, whereby its movement is restricted. As a result, damage to the gasket caused by deformation or play of the bearing case can be prevented, whereby the lifetime and reliability of the product are improved.
In addition, since the rib walls are provided in a side of a crankcase, a gap forming a part of an oil pan within the bearing case becomes small, so that it becomes possible to prevent the lubricating oil from entering the bearing case and thus the oil surface of the oil pan from lowering. Therefore, even if the engine is located with inclination, the oil dipper always sinks below the oil surface, thereby the lubrication to the valve-operating system can be stably ensured.